The field of the invention relates generally to reliability estimation, and more particularly to reliability estimation methods for large networked systems.
At least a portion of the aircraft industry is transitioning to composite airplanes. The aircraft that incorporate such composite structures have different electrical and conductive characteristics than do traditional aluminum or other metal structures. In particular, a current return network (CRN) is made necessary due to the use of composite structures, the CRN providing lightning protection and a ground electrical plane. However, the CRN needs to be certified and optimized as much as possible. Such a certification typically includes the safety assessment of the CRN which is done by means of reliability estimation for the CRN.
Commonly used prior solutions for estimating the reliability of an airplane system include using a fault tree method and a reliability block diagram method. The fault tree method is inadequate for at least two reasons. First, there is no automated translation of a large aircraft current return network into a fault tree model. The manual translations are prohibitively complex, error-prone, and are not practical to maintain. Second, currently available fault tree solvers are not capable of handling such a large fault tree model, even if one were manually generated.
The reliability block diagram solution is not adequate because of size and computational throughput limitations. In addition, creating a reliability block diagram for an aircraft CRN is as challenging as utilization of the fault tree method.
A Symbolic Hierarchical Automated Reliability and Performance Evaluator (SHARPE) package is a well known reliability and estimation tool in the field of reliability and performability, used by universities as well as by companies. A modeler who is familiar with many different kinds of models, can easily choose models that best suit a particular system and the kind of measure that is needed at each stage of the design. It is also possible to use different kinds of models hierarchically for different physical or abstract levels of the system and to use different kinds of models to validate each other's results. Steady-state and transient computations are available in the tool. The tool provides a modeling paradigm called the Reliability Graph which allows reliability modeling of a network system. However, a reliability graph solver in known versions of the SHARPE tool have not been capable of obtaining an exact solution for the large composite aircraft CRN model, in partdue to the large size of an airplane network CRN.